A novel spinal circuit involved in locomotion

描述（由申请人提供）：现代神经科学的一个主要目标是了解行为的神经元基础。运动是由复杂的神经回路在脊髓中产生的一种行为。它被定义为相对肢体之间以及同一肢体的对抗性肌肉之间精确，协调和交替的活动。此外，运动行为是有吸引力的实验研究，因为它可以很容易地访问，定义和量化。中间神经元网络，被称为中枢模式发生器（CPG），被认为是负责节律活动的起源。CPG神经元激活运动神经元，运动神经元反过来激活周围肌肉，导致运动。运动神经元还具有轴突侧枝，专门针对一类抑制性中间神经元，称为Renshaw细胞。我们最近的研究挑战了运动神经元仅仅是脊髓运动输出的传统观念。在胆碱能受体拮抗剂存在的情况下，刺激新生小鼠运动神经元轴突可触发运动活动。这表明运动神经元轴突侧支释放的乙酰胆碱不是节律发生所必需的。此外，我们发现除了乙酰胆碱外，新生儿运动神经元还从轴突侧枝（谷氨酸或天冬氨酸）释放第二种快速兴奋性神经递质。运动轴突的刺激如何触发新生儿脊髓的运动样活动的机制尚不清楚。识别

DESCRIPTION (provided by applicant): A major goal of modern Neuroscience is to understand the neuronal basis of behavior. Locomotion is a behavior generated in the spinal cord by complex neuronal circuits. It is defined as precise, coordinated and alternating activity between opposing limbs as well as between antagonistic muscles of the same limb. Furthermore, locomotor behavior is attractive for experimental study because it can be easily accessed, defined, and quantified. A network of interneurons, known as the central pattern generator (CPG), is thought to be responsible for the genesis of rhythmic activity. CPG neurons activate motor neurons which in turn activate peripheral muscles resulting in movement. Motor neurons also possess axon collaterals which target exclusively a class of inhibitory interneurons, known as Renshaw cells. Our recent studies have challenged the traditional idea that motor neurons are simply the motor output from the spinal cord. Stimulation of motor neuron axons in neonatal mice can trigger locomotor activity in the presence of cholinergic receptor antagonists. This suggests that acetylcholine released by motor neuron axon collaterals is not required for rhythmogenesis. Furthermore, we discovered that neonatal motor neurons release a second fast excitatory neurotransmitter from their axon collaterals (glutamate or aspartate) in addition to acetylcholine. The mechanisms of how stimulation of motor axons can trigger locomotor-like activity in neonatal spinal cords are not understood. The identification of neurons and their connectivity that participate in the locomotor CPG is critically needed for the elucidation of mechanisms involved in locomotor activity and would therefore represent a fundamental advance in the field. In this proposal, we provide some preliminary evidence that a novel class of excitatory interneurons is a critical component in a ventral spinal cord circuit, putatively connected to lumbar motor neurons and it may be involved in the locomotor central pattern generator. We have designed a set of experiments to test our main hypothesis, that motor neurons play an active role in the generation of locomotor activity. In Aim 1, we will attempt to identify the neuronal targets of this novel type of interneuron using physiological and morphological assays. In addition, we will investigate the participation of these interneurons in locomotor-like behavior using modern optophysiological methods employing the in vitro spinal cord preparation. Optophysiological approaches combine optical imaging with electrophysiological techniques. In Aim 2, we will perform laser capture microdissection from these interneurons compared to motor neurons using a differential gene microarray analysis. Validation of gene(s) expressed solely in these interneurons will be performed by in situ hybridization techniques. In summary, this two-year research project describes a comprehensive set of experiments that have the potential to identify a novel class of excitatory interneurons as a key neuronal player in the rhythmogenesis of locomotor activity.